<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .one {
      background-color: aqua;
      margin-bottom: 10px;
      width: 100px;
      height: 100px;
    }
    .two {
      background-color: aquamarine;
    }
    .subNode {
      width: 100px;
      height: 100px;
      background-color: bisque;
    }
  </style>
</head>
<body>
  <div class="one" id="anotherSub"></div>
  <div class="two" id="parentNode">
    <div class="subNode"></div>
  </div>
  <button id="append">append</button>

  <script>
    var obj = document.getElementById('append');
    obj.onclick = function () {
      var parentNode = document.getElementById('parentNode');
      var anotherSub = document.getElementById('anotherSub');
      parentNode.appendChild(anotherSub)
    }
  </script>
</body>
</html>